For use in laundry detergent formulations, personal care products, and in crop protection, there is a great multiplicity of nonionic surfactants. One alternative to many conventional surfactants are polyhydroxy-fatty acid amides, which are valuable surface-active compounds with diverse possible uses.
They can, for example, be used—as they are or in a mixture with anionic, cationic and/or nonionic surfactants—as cleaning agents, laundry detergents, textile treatment agents or the like, and can be used in the form of solid products (for example, as powders, granules, pellets or flakes), solutions, dispersions, emulsions, pastes, and the like. Since polyhydroxy-fatty acid amides are also highly biodegradable and can be prepared from renewable raw materials, they have acquired greater significance in more recent times.
The obvious supposition would therefore be that these compounds have found application in a multiplicity of formulations. However, it is not possible to confirm this supposition. As a reason for this fact, it is assumed that the preparation of these polyhydroxy-fatty acid amides, particularly in the desired quality and purity, is too demanding. The batch-process preparation of polyhydroxy-fatty acid amides has indeed been copiously described, but these processes result in unsatisfactory quality. For use in the personal care segment in particular, a strict specification must be complied with in relation, for example, to color, solvent content, and secondary components. This is not possible by an economic route with the processes described in the literature. In particular, high residence times with severe temperature exposure, poor mixing, and severe foaming in a batchwise-operated process may give rise to considerable problems.
Preparation in a batch process allows the various requirements to be addressed specifically during the reaction. Thus there may be different rheological phases, lasting for different lengths of time according to product. A continuous process has to master this challenge, and this is one reason why to date there have been no continuous processes described that achieve the stated quality requirements.
EP 0633244 A2 describes the operation of a stirred tank cascade for the preparation of polyhydroxy-fatty acid amides. That operation, however, has the disadvantage of a broad residence time distribution, leading to increased formation of undesirable byproducts. In view of the high reaction volumes and associated adverse temperature distribution in the reaction system, the thermal exposure is too high, with adverse consequences for the color of the products.
This operation, moreover, has the disadvantage of severe foaming during the removal of the coproducts. As a result of the foaming, the desired low pressure for complete removal of the coproducts cannot be attained. In order to ensure removal of the coproducts, it would be necessary to use a higher temperature and/or a lower throughput, resulting in a higher temperature exposure of the end product. High temperature exposure, however, leads to a greater amount of secondary components and to a poorer color.
In order to overcome the problems identified above, a new, continuous process has been developed in which polyhydroxy-fatty acid amides can be prepared with improved quality and in greater yields by virtue of a shortened residence time and optimized temperature control. The improved quality is evident not least in a reduction of coloring substances and of secondary components (GCN<3, cyclic material <0.1%). With the new process, furthermore, it is possible to ensure an MeOH content of <0.3% in the end product.